Kessler Camera Crane Motion Control
Reliable, Consistent Motors and Careful Engineering Yield High-Performance Camera Positioning Systems, at an Affordable Price.
Location, location, location. It's not just a real estate mantra; camera positioning can make or break a shot. Feature filmmakers have the luxury of working with dollies and grips and expensive automated technologies to guarantee accuracy and repeatability of camera angles. Videographers aren't so lucky. With users ranging from bloggers to entertainment channels, to scientists and engineers, the video market presents the same positioning requirements but with only a fraction of the budget. That used to mean performance compromise - and then camera support system specialist Kessler Crane came along. The company puts the focus on developing affordable positioning systems that still give users the power to create the shots they need. With the help of sophisticated engineering, plus small DC motors from MICROMO that provide high-end results at a low-end price, Kessler Crane takes economical performance to a whole new level. "We"re actually one of the least expensive motorized heads on the market in the professional category and we're doing things that nobody else is doing in terms of features," says Eric Kessler, president and founder of Kessler Crane. "I think the cheapest head that [we feel] outperforms us costs $5000 to $10,000, and we&'re doing it for [under $1900], so we're doing quite a bit with what we have."
Video applications can vary from filming a sporting event to performing time-lapse video of a botany experiment. That means the same positioning system needs to be able to make a lightning quick 180˚ pan to track a hockey puck speeding over the ice or slowly turn 15˚ to 20˚ degrees over a row of plants. It has to provide not only broad range of motion but high dynamic range, while operating with the lowest possible audible noise - and at the lowest possible price.
Balancing these conflicting demands presented a significant challenge but the Kessler Crane design team rose to the occasion. The company offers two types of motion systems for video cameras: a pan-tilt unit called the Revolution and a narrow-rail automatic-dolly system known as the CineSlider. The pan-tilt unit consists of a two-axis system powered by M32P gearmotors from MICROMO’s Micro-Drives line. With a 516:1 reduction ratio, the units can provide 4 Nm of torque. To achieve the extreme range of motion, the engineers built the unit with a hollow axel, running the wires up through it. That eliminates windup and allows the Revolution to pan better than 360° in each direction. Velocity varies from one revolution in 3.8 s to one in 10 min. 40 s.
The slider features a 4- to 5-inch wide rail system that mounts on top of a tripod and typically runs 3 to 5 ft. The automatic version combines another M32P gearmotor with Kessler Crane’s purpose-built Oracle controller to command the unit in realtime by joystick. Velocity varies from 12 in./s to 12 in./3+ years in time-lapse mode.
The initial design goal was to product a system capable of ultralow-speed motion. The problem is that at a very low speeds, most motors suffer from cogging. After looking around at their options, the team chose a MICROMO motor with a fivesegment commutator rather than a three-segment commutator design, which helped minimize the effects of cogging. That took care of low-end velocity, but same motor needed to also be able to follow the speeding hockey puck. Getting sufficiently high-velocity operation remained a challenge until engineers tried briefly and intermittently overdriving the 12-V motor at 24 V. Because the system gets a boost for only 10 or 15 s at a time, and only when the load is already moving, the technique does not significantly degrade motor lifetime, especially for the kind of low duty cycles presented by video applications. “We did some testing to make sure they would survive,” says the design engineer. “[We] ran one motor at 36 V for an hour. That’s equivalent to years of use in this product.”
One of the key requirements from the system was backlash-free motion. Although backlash-free motors are available, the price tag was too steep for the type of highly affordable system Kessler envisioned. The team developed a clever alternative. Instead of a single expensive, high-performance motor, they chose a pair of MICROMO’s economical DC micro motors, set to run slightly opposed in a masterslave configuration. When properly coupled together, with the aid of fairly sophisticated software, the slave motor pulls the slack from the system. “What we found was that with two economical motors, we could make them perform even better than a high-end, lowbacklash motor, and we got our system to a third of the price by doing it that way,” says Kessler.